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Research on Underwater Acoustic Communication and Underwater Positioning Systems for Underwater Drone Control
Get PDFRecent advances in underwater applications, such as ocean remote operations and network sensors, have created a critical need for high data-rate and robust underwater wireless communications. Due to significant attenuation of electromagnetic or radio waves in water, many applications require mid- to long-range underwater communications, which can only be achieved through acoustic waves. However, the underwater acoustic environment presents challenges such as limited bandwidth, timevariability, and frequency-selectivity, which severely restrict acoustic communications.
The ultimate goal of this research is to recognize the use of automated drones in the marine industry, which is expected to grow in the future, especially underwater. Underwater, radio waves cannot be used and wireless communication can only be realized by using sound waves or light. Additionally, light cannot penetrate turbid conditions and can only be used in limited situations. In order to recognize autonomous drones underwater in various applications, it is necessary to successfully apply acoustic technology. Hence, the aim of this research is to develop a key device that combines underwater acoustic communication with acoustic positioning technology, enabling autonomous operation of underwater drones for various applications such as offshore wind power generating maintenance and marine aquaculture monitoring. A specialized positioning technology for ocean map measurement that evolved to recognize the self-sustaining operation of underwater drones is being developed and will evolve this technology to recognize autonomous operation of underwater drones targeting general applications. This research also has the intentions of developing a low-cost and compact AUV that can operate effectively in shallow and deep water, which presents substantial challenges for both the system design and the intended applications.
This research focuses on tackling two challenges. (1) To increase MAVLink packets for sending and receiving data for our Underwater Communication System and (2) to propose a new Underwater Swarming AUV Communication System for two reference points underwater positioning. The research presented the Ocean Experiment of the 2 reference points and for further improvement, we investigated on 3 and 4 reference points based on simulations.
The first challenge is to establish underwater acoustic Micro Air Vehicle Link (MAVLink) communication for swarming Autonomous Underwater Vehicles (AUVs) between the Mother Ship and the AUV via the MAVLink protocol. This involves developing a reliable communication system that enables effective coordination and information exchange between multiple AUVs in an underwater environment. This work focuses on leveraging underwater acoustic communication as a means to enable effective communication and coordination among the AUVs.
MAVLink is designed to be simple, efficient, and extensible, making it suitable for a wide range of unmanned vehicles. One issue is the communication between MAVs in order to coordinate tasks and obtain necessary information from them. Just like in the human world, a common language is necessary for a conversation. A standardized swarm communication protocol for MAVs is necessary for communication in heterogeneous settings. For our underwater acoustic MAVLink communication system, we adapted the MAVLink protocol to support the communication between the Base Station (BS) as the QGC (QGround Control), and the Remote Operated Vehicle (ROV) as Ardupilot. Because the aim for this experiment is to make communication between the BS and ROV, we encoded the MAVLink messages into acoustic signals to propagate though water and be received by the underwater vehicle or vice versa.
In this experiment, we made an assumption for the communication between the BS and the ROV. Instead of actually operating the drone, we simulated the actual drone operations using Software-In-The- Loop (SITL simulator), and mock ROV component in a bucket. There were four case scenarios in which were performed successfully using the MAVLink protocol; (1) Wired Local Area Network (LAN) connection communication between QGC and ArduPilot, (2) Wired LAN connection communication between PCs using MatLab UAVTools, (3) One-way communication experiment by inserting an underwater wireless communication device between PC-to-PC, and (4) Two-way communication experiment. Communication connection was confirmed and data packet was increased making the experiment a success.
The second challenge is to develop an Underwater GPS (Global Positioning) System specifically designed for Autonomous Underwater Wireless Drone Control.
This involves creating a system that can accurately determine the position and location of underwater drones without relying on traditional GPS methods, which may have limited availability and reliability underwater. To overcome this challenge, this work focuses on the requirement of the development of innovative techniques and technologies to achieve precise and reliable drone control in an underwater environment. Devising an effective underwater positioning system enables autonomous control of underwater drones.
The ability to navigate effectively poses a significant obstacle in utilizing AUVs to tackle crucial societal issues. Precise navigation data is indispensable for ensuring the safe operation and retrieval of an AUV. GPS-GNSS provides global positioning accuracy when the AUV is close to the water's surface. LBL method provides high accuracy and precision in positioning which is suitable for larger areas. Fixed-Triangular Position provides accurate positioning within the range of the reference points. The experiment was based on 2, 3, and 4 reference points which is suitable for smaller area. Furthermore, the accuracy of the data collected by an AUV relies on knowing the exact location from which it was obtained. Because the aim for this research is develop a device that combines underwater acoustic communication with acoustic positioning technology, we developed a specialized positioning technology for ocean map measurements using the combined methods.
For this experiment, the proposal for a new two reference point underwater positioning system and the ocean experiment is presented. Investigation on a three and four reference points based on simulations for improvement is also provided. We set the targeting area within a fixed-triangle area and to determine the position of a point, it is measured by the distances from two or more reference points. In other words, each AUV can individually measure the lengths. Once those lengths are known, based on the position information, each AUV can calculate all AUV positions. Our system utilizes GPS-GNSS for surface operations, LBL for high-accuracy underwater positioning, and INS for continuous navigation in GPS-denied environments. In addition to Kalman filtering to enhance accuracy and robustness even further. This can fuse data from multiple sources using this technique. The modeled system can operate at a depth of 80m and a range of 100m.
This research also has the intentions of developing a low-cost and compact AUV that can operate effectively in both shallow and deep water, and short-to-long ranges, which presents substantial challenges for both the system design and the intended applications. In other words, everything that was used to built the communication systems (air, land, and underwater), software/hardware systems, protocols, and methods were all cost-effective.博士（工学）琉球大
需要側管理を考慮したマイクログリッドの多目的最適容量と電カ計画
Get PDFMicrogrid is the brightest solution to overcome the energy problems of the newly constructed areas. Multi-objectiveoptimal microgrid sizing plays a technical·economical·environmental role in designing sustainable and reliablepower systems. In order to reduce CO2 emissions, depending on renewable power sources is the best option to reachthis target. Hybrid renewable sources with st.orage facilities help in reducing renewable sources'uncertainties.Connecting the microgrid to the public grid ensures the full system reliability and increases the system productivityby selling extra power back to the utility. System productivity can be increased by selling extra power to the grid,integrating electric vehicles or using excess power in other ways like seawater electrolysis. For any practicalmicrogrid, energy management strategies are crucial for a feasible design. Demand response programs offer anenergy management technique for managing electrical consumption. It is one of the load·side management schemesthat assists in rearranging the load by transferring a portion of it from peak t.o off-peak periods. The integration ofelectric vehicles into microgrids also provides an effective means of energy management. Moreover, replacing ICEcars with electric vehicles reduces emissions, especially if they are charged from renewable sources. Theincorporation ofEVs into microgrids via vehicle·to ·grid strategies has a significant impact on reshaping the load,increasing revenues, and supplying power in the case of outages or a lack of generation. This study introduces astudy of optimal power scheduling and energy management of hybrid residential microgrids. It discusses differentscenarios of the system with different configurations and renewable technologies, considering renewable sources'uncertainty. Moreover, different generation and storage systems are considered, like PV, WG, biomass, fuel cells,seawater electrolysers, BESS, public grid, and EVs. Different multi-objective optimization techniques are introducedto satisfy the optimum system cost with minimum emissions and loss of power supply. Furthermore, a comparisonbetween different EVs integration and V2G techniques is explained. By managing charging and discharging ofEVs,both micro,grid and car owners can make reasonable revenues. Besides that, it provides the ability to change thedemand patterns to satisfy the other microgrid's objectives. Time·of·use demand response is also applied as it hasan effective role in load reshaping to maximize use of renewable sources, reduce the peak load, and lessen the grid'semissions. The obtained results verified that load reshaping techniques provide an effective control option for powernetworks to economize total cost, increase revenues, and educe em函ions. This can be done effectively by usingV2G and DR techniques with the help of renewable energy sources. It also confirms the effectiveness of biomass toensure system reliability and reduce grid emissions.博士（工学）琉球大
持続可能な開発のための離島におけるハイプリッドマイクログリッドの最遁容量と性能解析
Get PDFThe microgrid powered by renewable energy, especially for distant places, is attracting interest from the global power generation sectors. There are several reasons to increase the amount of renewable energy in the microgird. The cost of fossil fuels is rising as a result of rising electrical consumption. On the contrary, this over use of fossil fuels is contributing to global warming and the depletion of natural resources like fossil fuels. Therefore, it is important to switch from fossil fuel to renewable energy sources in order to limit the usage of fossil fuels. Distributed generation systems (Di Gs) based on renewable energy are becoming more and more common. In the upcoming energy market and demand, DiGs are anticipated to be extremely important. The energy sources used in DiGs include wind generation (WG), photovoltaic (PV) generation, concentrated solar power (CSP), biomass power generation, hydroelectric and geothermal plants, smart homes, and battery energy storage systems (BESS). If these DiGs are operated correctly, they can provide a number of advantages, including increased reliability. On the other side, there are issues with the high initial investment cost and the unpredictable output power of renewable energies in various weather scenarios. However, power producers should take into account optimization techniques for minimizing operational expenses and maximizing re.venues as well as taking into account the value to customers. Due to the high cost of installing renewable energy technologies, utility companies must determine the life cycle cost (LCC) or net present cost(NPC).
First of all, the thesis describes the optimization of the cost and carbon emission function of a hybrid energy system comprising PV, WG, BESS, and diesel generator (DiG) at Aguni Island, Japan, using a multiobjective optimization model. To solve the proposed problem in the presence of advanced direct load control (ADLC), the_ -constraint method and mixed integer linear programming (MILP) are utilized. After obtaining all possible solutions, the fuzzy satisfying method (FSM) selects the best possible solution among all solutions. The main purpose of this part is to cope with the output power uncertainty of renewables by considering ADLC, residential PV, and BESS at the lowest cost and with the least amount of carbon emission, while putting less burden on consumers by minimizing the interruptable load (IL). Then, this thesis explores Bangladesh's present energy condition, renewable energy (RE) possibilities and designs an optimal 100% RE-based off-grid power system for St. Martin's Island, Bangladesh. The optimal size of a hybrid renewable microgrid based on photovoltaic (PV) cells, a battery energy storage system (BESS), fuel cells (FC), and an electrolysis plant (EP) is proposed. ADLC and rooftop PV meet the energy demand at the lowest cost, and profits are maximized by selling chemical products produced by seawater electrolysis. Four cases are explored with the MILP optimization technique using MATLAB software to demonstrate the efficacy of the suggested power system.
Furthermore, the techno-economic potentiality of various system configurations is demonstrated using HOMER software and a PV/WT/battery/DiG-based optimal system is chosen for the selected off-grid area based on NPC. The result of this optimal system is compared with the result obtained by MILP. Due to lower NPC and carbon emissions, MILP-based systems are more cost-efficient and eco-friendly. A sensitivity analysis of uncertain parameters, including annual load, discount rate, fuel price, and solar radiation, has been added to evaluate the effect of the variation of these parameters. Additionally, a few linguistic factors, such as land usage,'future of technology, employment, comfortable living, and biological diversity, are also examined by normalization to demonstrate the efficiency of the optimal system. The 0ptimal system achieved top ranking for its outstandi.ng preference values in all criteria except land usage and is recommended in the environmental, technological, and social categories. Finally, all the proposed methods are summarized. Scopes of future research have also been described.博士（工学）琉球大
Foraging ecology and life history strategy of goatfish （Mullidae） in coral reef waters
No full textヒメジ科魚類は，世界中の温暖な海に生息しており，現在6属80種以上が報告されている．沖縄島周辺海域には，3属約20種が分布しており，電灯潜り漁，刺網漁，定置網漁等で漁獲され，重要な水産資源として利用されている．しかし，沖縄島周辺海域において，本科魚類の資源管理に重要な寿命や成熟サイズ等の生物学的基礎情報は欠落している．また，本科魚類は，下顎に一対の鬚を持つことが形態的特徴として挙げられる．この鬚には，味蕾に類似した感覚器が並んでおり，鬚を利用して餌生物を採餌することが知られている．しかし，鬚を使った特異な採餌生態を持つにも関らず，食性や採餌行動と鬚の形態の関係性については，ほとんど研究されていない．そこで本研究は，沖縄島で一般的な6種（ホウライヒメジ，コバンヒメジ，オジサン，アカヒメジ，モンツキアカヒメジ，ヨメヒメジ）の年齢，成長および繁殖特性の解明を試みた．さらに，ヒメジ科魚類15種の食性解析，12種の採餌行動の観察を行い，これらの採餌生態と鬚の形態との関係性について検討した．また，これらの採餌生態が，ヒメジ科と他魚種の種間関係構築にどのように作用しているかを検証した．
耳石を用いて年齢査定を行った結果，いずれの種も最高齢が6歳前後であり，他海域におけるヒメジ科魚類の報告と類似した．一方，最大体長には，種ごとに大きな差がみられ，本科魚類は，成長速度に大きな違いがあると考えられた．また，同年齢階級で比較すると，ウミヒゴイ属は雄が雌より大きいのに対し，アカヒメジ属とヒメジ属は雌が雄より大きかった．ウミヒゴイ属は，ペア産卵を行う種が多いことが知られており，繁殖に雄の体長が大きいことが有利に働く可能性がある．一方，アカヒメジ属の成熟した精巣は他の属に比べ大きいことから，アカヒメジ属はランダム配偶である可能性が高い．このような繁殖生態の違いが属ごとの成長パタンに影響していると考えられた．
食性解析と採餌行動の観察を行った結果，本科魚類は属に関係なく，種ごとに様々な食性，採餌行動を示した．さらに，日中に摂餌を行う種と夜間に摂餌を行う種がいることが示唆された．鬚の形態が類似した種同士では，食性と採餌行動および採餌基質の嗜好性が類似する傾向にあった．例えば，鬚が太い種は，胃から砂と共に多毛類や甲殻類が主な餌生物として出現した．さらに，これらの種は，砂地の中に吻を押し込み採餌していた．鬚が細い種は，砂地の表層や，ガラモ，サンゴ等の複雑な構造をした基質に対して採餌がみられ，甲殻類や魚類を捕食していた．つまり，鬚の形態は，採餌行動と採餌基質に影響し，それらが食性に反映されると考えられた．種ごとに食性，採餌基質，摂餌時間が異なったことから，餌資源の重複や競争を避けるために，“棲み分け”，“食い分け”，“時間分け”が行われている可能性が示唆された．ヒメジ科の採餌行動観察を進める中で，同種で群れを形成する種と他種と行動する種に分類できた．鬚が太く，砂中を採餌する種は，フエフキダイ科などと行動する傾向が強いことから，採餌生態が種間関係構築に影響を及ぼしていることが示唆された．一方，それ以外の種は，集団での狩りや，夜間に分散して採餌することで，同種間の餌の競合を少なくしていると考えられた．
食性，採餌行動および採餌基質は，形態に影響を受けるにも関らず，それらは属内で多様であったのに対し，成長の雌雄差と繁殖生態は，属内で類似した特徴を示すと考えられた．既存の分子系統解析結果に当てはめると，本科魚類の採餌生態は，種が分化した後に多様化した形質であることが示唆された．Goatfishes (Mullidae) are widely distributed in warm marine water throughout the world and are a commercially important fish family. This fish family is comprised of more than 80 different species in 6 genera. About 20 mullid species can be found in Okinawa Island, Japan, where all species are exploited as a food resource. Fishes are captured by night spear-fishing, set net and gillnet. Despite their importance as a marine living resource, life-history traits of goatfishes have not been studied yet in detail in Okinawa Island. One of the morphological characteristics of goatfishes are their paired chin barbels containing taste buds. It is known that goatfishes are using those barbels for detecting hidden prey organisms. Thus, variation in the morphology of barbels among species might be associated with differences in their diet. However, few studies have so far been conducted on a possible relationship between species-specific diet and the morphology of barbels. In order to understand the feeding ecology of goatfishes, stomach contents of totally 15 species and foraging behavior of totally 12 species were investigated. Furthermore, basic biological information such as age, growth and reproductive biology of 6 common species of 3 genera (Parupeneus ciliates, P. indicus, P. multifasciatus, Mulloidichthys vanicolensis, M. flavolineatus, Upeneus tragula) were examined.
To estimate age and growth of mullid species, sagittal otoliths were transversionally sectioned. Distinct opaque bands were assumed to represent growth rings and therefore counted. To validate the periodicity of growth ring formation, monthly changes in occurrence of opaque bands on the edge of each otolith were determined. Opaque rings appeared annually and were most frequent either during the spawning season or before it. Standard length and age data were fitted to the von Bertalanffy growth equation. The result of present study showed that the maximum age for all the species was ca. 6~8 years. This was similar to maximum ages observed from other fish studies in marine waters. However, high variation in maximum length between species was observed indicating that the growth rate differed interspecifically. In Parupeneus, males usually grew larger than females in the same age class, but males of two Mulloidichthys species and males of U. tragula were smaller than the females of the same age class. It is known that species in the genus Parupeneus perform pair spawning. Our findings suggest that the observed size differences between males and females might be related to the genus-specific spawning mode. Spawning season and maturation size were estimated according to histological observation of gonads. Main spawning season of 6 species was estimated to be in spring or summer. In the genus Parupeneus, 50% of mature females and males had similar size or the males were larger than thefemales. Contrary, maturation size of females in the genus Mulloidichthys and in U. tragula was larger than the maturation size of males. Histological observation of ovaries and frequency distribution of oocyte diameter indicated that two Mulloidichthys species had group-synchronous oocyte development, but species from the genera Parupeneu and Upeneus showed asynchronous oocyte development. In addition, estimated female fecundity in the genus Mulloidichthys was greater than in the other genera Parupeneus and Upeneus. These results indicate that reproductive biology is similar among the species of same genus, but differed among genera.
An examination of totally 1,110 stomachs and totally 21 hours of foraging behavior observation were conducted. Regardless of the genus, a variety of feeding habits, foraging behavior and preferences of substrate were observed. In addition, some species were found to feed mainly at nighttime. Generally, species with similar barbell morphology exhibited similar feeding habits. For example, species with thick barbels were predominantly feeding on polychaetes or crustaceans and their stomachs usually contained high amount of sand, which was associated to their feeding behavior (plunging of the snout into the sediment while feeding). Species with short and thin barbels were observed to forage on sandy bottom, inside or on the surface of macroalgae stands and their diet was mainly comprised of crustaceans. On the other hand, P. cyclostomus was the species found to be piscivorous searching its prey in structurally more complex habitats such as coral colonies or rocky crevices. In summary, the morphology of barbels was strongly related with foraging behavior, associated substrate of feeding, which in turn reflected the feeding characteristics of each goatfish. The observed differences in feeding ecology might be the result of an interspecific diet competition, i.e. to avoid diet overlap among species. In the course of observing the foraging behavior of Mullidae, we were able to classify them into two groups: species that form groups with the same species and species that behave with other species. Species with thick barbels that forage in the sand tend to swim in small groups with Lethrinidae and Labridae. On the other hand, other species tended to cluster with their conspecifics, but they were thought to reduce competition for food among conspecifics by hunting in groups and foraging dispersedly at night.博士（理学）琉球大学University of the Ryukyu
アオリイカ における視覚的左右性とその機能
Get PDFLateralization is left right asymmetry of behavior and morphology , which appears in many animals ranging from invertebrates to vertebrates. L ateralization provides animals advantage for some features such as neural processing in brain hemispheres, rapid decision making, and synchronization of individuals in a group. Coleoid cephalopods (squid, cuttlefish, and octopus) that possess vertebrates like lens eyes and extremely large brain amongst invertebrates show sophisticated visual behaviors such in hunting, vigilance, or intraspecific communication. Cephalopods also exhibit the lateralization as in other animals but its details and adaptive function have not been well documented . In this study, I investigated the ontogeny and possi ble function s of the lateralization for the vision in the oval squid Sepioteuthis lessoniana with assumption of superorganism vision acting in a social school that this squid usually forms . In Chapter 2 , I examined the ontogenetic association s between th e schooling behavior and the lateralization for the vision of squid (Fig. 1). I found that the vis ion and optic lobes , a region that controls visual perception are lateraliz ed, and side and strength of its lateralization change s while squids grow and exhib it the schooling behavior. In Chapter 3 , I examined the ontogenetic association of the eye s and optic lobes in relation to the lateralization of squid . I found that the left and right eyes symmetrically develop whereas the left and right optic lobes asymme trically develop (Fig. 2). In Chapter 4 , I examined the association between t he individual variation of visual lateralization and the five temperament traits (activity, aggressiveness, exploration avoidance, shyness boldness, and sociability) of squid . I f ound that the se temperament s were expressed regardless of visual lateralization with wide individual variation . In Chapter 5 , I examined whether the visual lateralization relate s to the selection of individual position within a school of squid. I found that the strength of visual lateralization is associated with the left and right position s of individuals within a school (Fig. 3)3). In Chapter 6 , I examined the role of the visual lateralization on the school formation of squid using computer simulation . I found that the interindividual variation of the visual lateralization is associated with the formation of their s chool. According to these results described , I concluded that the oval squid create the superorganism vision by th eir visual lateralization, and due to this system, t hey can effectively attack and defend to survive.左右性とは行動や形態に見られる左右非対称性のことであり、無脊椎動物から脊椎動物まで幅広く存在する。左右性を有することは、神経処理コストの軽減、速い意思決定、他個体との効率的な行動同調などの利点がある。ツツイカ類、コウイカ類、タコ類を含む頭足類鞘形類 は脊椎動物と類似なレンズ眼および無脊椎動物の中で最大の脳を有する。それらに伴い頭足類は、捕食、警戒、種内コミュニケーションのような様々な視覚的行動を示す。頭足類 も視覚に関する左右性を有するが、 その適応的機能は詳細に調べられていない 。 本研究では、ツツイカ類の中でも高い社会性を有するアオリイカ Sepioteuthis lessoniana ) を対象に、視覚に関する左右性が群れ行動において 超個体視覚として機能するという仮説を立て、その検証を行った。 はじめに、群れ行動の発現過程と視覚に関する左右性の発現過程との 関係を調べた。その結果、視覚に関する左右性が群れ行動の発現過程と連関して変化することが明らかとなった。次に、眼球と視葉 の 容積 における相対成長 を調べた。その結果、 眼球は 視葉よりも早く成長するが、 左右対称に成長 し、それに対し 視葉は左右非対称に成長することが明らかとなった 。次に、 視覚的左右性の個体差 と気質との関係性 を調べた。その結果、気質と視覚的左右性 に関係が見いだせず、それらの個体差は 独立して出現することが 示唆された 。次に、 視覚的左右性 と 群れ内の位置 との関係 を調べた。その結果、視覚的左右性 の強さ が特定の場面にお いて 群れ内の位置決定に関与することが考えられた。最後に、 シミュレーションを用いて 群れ形成における視覚的左右性の役割を調べた。その結果、群れ内の視覚的左右性の 個体差 が群れ形成に重要であることが示唆された。以上の実験から、アオリイカの視覚に関する左右性が 超個体視覚を作り出し、生存のために効率的に攻撃および防衛することができることを結論づけた。博士（理学）琉球大学University of the Ryukyu
米軍統治下の沖縄における沖縄人メイドに関する研究
Get PDFThe purpose of this dissertation is to demonstrate how Okinawan maids working for American-military-related personnel during the period of American control were not simply victims of their circumstances. Through primary source materials and oral histories this paper will demonstrate how beyond the struggles they faced, maids in Okinawa empowered themselves through educational and cross-cultural opportunities to improve their lives. After the introduction in the first chapter, the second chapter provides background information explaining how and why Okinawan maids came to exist in such large numbers in post-war Okinawa. The third chapter focuses the struggles and hardships faced by Okinawa maids. Unprotected by legislative regulations, they were paid low salaries, worked long hours, and could be fired at the whim of their employer. They also faced sexualization and cases of physical harm at their workplaces. Yet, these experiences do not encapsulate the entirety of their experiences. Chapter four focuses on how through access to a wide variety of vocational training programs, maids and the women wanting to become maids in Okinawa, empowered themselves through training programs. Through enrollment in these programs not only did these women become more proficient employees, but they were also able to learn a variety of skills that were new to women in post-war Okinawa. Maids were able to utilize these skills to not only improve the overall image of a maid in post-war Okinawa but to also create improved job opportunities for Okinawan women. Chapter five focuses on how maids were leaders in the cross-cultural exchange process with their American employers. Using the lens of a “contact zone,” this chapter demonstrates how through a process of transculturation, Okinawan maids actively accepted and rejected American culture. Through this process they became comparatively knowledgeable in American culture. The chapter also illustrates how Okinawan maids, who were viewed as subservient to the U.S. rule, played a significant role in humanizing the Okinawan population to Americans and enriching Americans understanding of the history and culture of Okinawa, demonstrating the knowledge and power maids held. Chapter six concludes the dissertation. This study of Okinawa’s maids demonstrates how these women found ways to empower themselves in a seemingly powerless situation in post-war Okinawa. Instead of simply being a footnote in Okinawa’s history, maids can be seen as a symbol of the ingenuity and resourcefulness of Okinawan women in American controlled Okinawa.この博士論文の目的は、沖縄の米軍統治時代に軍関係者のもとで働いていた沖縄のメイドの歴史とその職業が沖縄の女性に与えた影響を明らかにすることである。一次資料やオーラルヒストリーを通じて、沖縄のメイドが苦難を克服し、訓練や異文化交流の機会を通じて、いかに自分たちの生活を向上させることができたかを説明する。第1 章の序論に続き、第2 章では、戦後の沖縄でメイドが存在するようになった経緯や背景を説明する。第3 章では、沖縄のメイドが直面した苦難を明らかにする。沖縄のメイドは、法律的な保護がなく、低賃金、⾧時間労働、不当解雇などの不利益を受けることがあった。また、職場で雇用主の性的対象になったり、身体的な危害に直面することもあった。しかし、これらは、メイドの経験の全てではない。第4 章では、沖縄のメイドやメイドになろうとする女性たちが、さまざまな職業訓練を利用することで、自分たちの力を高めていた側面に焦点を当てる。メイドたちは、職業訓練で得たスキルを活用することで、戦後の沖縄におけるメイドという職業のイメージを向上させるだけでなく、沖縄の女性たちの新しい雇用の機会となった。第5 章では、「コンタクト・ゾーン」の概念を援用し、メイドが仕事を通して琉米の文化交流のリーダーになったことに焦点を当てる。沖縄のメイドは、アメリカにとって被支配者であった沖縄の人々が、支配者と同等であるということをアメリカ人に理解させると同時に、アメリカ人が沖縄の文化や歴史に関心を抱くきっかけを与える役割を果たした。本博士論文では、戦後の沖縄において、一見無力に見える彼女たちがいかにして自らの能力を高め、女性として生きる力を獲得していったかについて記述した。沖縄の歴史の中で、メイドは米軍統治時代にあった沖縄の女性たちの創意工夫と機知を示すシンボルとして見ることができるだろう。博士（学術）琉球大学University of the Ryukyu
継続的な温度ストレスに対する造礁サンゴウスエダミドリイシの初期生活史から成体時期の順応に関する研究
Get PDFWith increasing seawater temperatures, coral reef ecosystems are declining at an alarming rate, which is one of the growing concerns with their early life stages. Anthropogenic climate change is increasing the frequency and severity of temperature anomalies, resulting in massive coral bleaching events that are bound to happen globally as a 1 4 °C rise in ocean surface temperat ure has been predicted within the next few decades. The prolonged bleaching significantly affects the overall health of coral reefs, resulting in the death of the coral host and, subsequently, reef degradation worldwide. However, whether reef corals and th eir next generation will acclimatize and adapt to such unprecedented stresses is an open question due to mixed and opposite responses that reef building corals showed under elevated temperatures. This thesis investigates the physiological reactions of accl imatization in adults and the early life stages of the broadcast spawner A. tenuis in Okinawa, Japan, and whether adult colonies and their next generation acclimate to consecutive thermal stress. Acropora tenuis was selected as a model species, the most ab undant species in the Indo Pacific region, and lives on shallow inshore coral reefs, where there are more significant temperature fluctuations. This dissertation documents the following results. Colonies could not tolerate consecutive thermal stress. Surpr isingly, colonies that experienced heat stress developed tactics to increase their fitness, exhibiting thermal acclimation. We also found that acquiring symbiotic algae during the larval stage will help the survival and growth of juveniles at normal temper atures. Still, these juveniles could not acclimate under thermal stress . Overall, these findings indicate in this thesis that despite adults and juveniles of Acropora tenuis being more sensitive to consecutive thermal stress but providing promising eviden ce for the ability of colonies to manage rapid climate change.博士（学術）琉球大学University of the Ryukyu
モンゴルにおける系統連系住宅用太陽光発電システムに関する研究
Get PDFMongolian residential sector including houses and Gers, which are traditional dwellings, becomes not only the biggest energy consumer but also produces the highest share of emissions because of the significant increase of utilizing traditional stoves with solid fuels such as charcoal and wood in wintertime. The aim of the thesis is to seek possibilities of a grid-connected solar photovoltaic (PV) system for Mongolian houses/Gers so as to improve the access to electricity and reduce greenhouse gases simultaneously. Solar PV system is considered as ease of installation, less maintenance and the absence of rotation.
Moreover, utilizing the proposed system provides the residents much more opportunities such as self-usage and trading the surplus energy to the grid. Due to the mismatch between PV array production and demand, the necessity for battery storage systems increases. Therefore, the battery storage system is included to increase self?consumption. However, depending on tariff structure, consumption, and production, the availability of the systems might be adapted.
This dissertation seeks to investigate the possibilities of deploying the grid-integrated residential PY-battery system for Mongolian houses and develop a viable configuration. To investigate the possibilities of the PY-battery system for Mongolian conditions, to begin with, we investigated the current electricity tariff market, household load consumption, and PV generation potential. A simulation model including the PV array, battery storage system, and load for the private house/Ger is developed with historical data. A simple operation strategy based on FIT tariff mechanism using PSIM software is studied. Thereafter, the impacts of numerous households with the PY-battery system on the low-voltage network were investigated. This can be implemented effectively in Mongolian households. It confrrms that tons of harmful emissions can be reduced.博士（工学）琉球大
A Study of Ethnic Homogeneity and Urban Planning in Kabul City, Afghanistan: Understanding and Planning the Cultural Fabric of Multi-ethnic Urban Areas through Communal Identity, Division, and the Roles of Community Facilities
Get PDFThe ethnic makeup of Kabul, the capital of Afghanistan, is diverse, with Pashtun, Tajik, Hazara, and Uzbek ethnic groups making up the majority. These distinct culturally rooted groupings are further split based on where they are from geographically within the nation. Following the civil war (1992?1996), which fueled ethnic polarization and spawned strategic clusters within the city, these differences have grown even more prominent. The current study examines ethnic segmentation in Kabul City, particularly emphasizing how historical and modern urban planning initiatives have addressed these disparities. We began by thoroughly assessing the literature on ethnic segregation in urban areas and the existence of ethnic and sub-ethnic groupings in Afghanistan. A化er that, we looked closely at Kabul's formal planning history and considered how the government dealt with ethnic segmentation and urban development. According to our research, smaller sub-ethnic communities are created due to people migrating from rural areas and the return of immigrants. These groups of people are connected by a shared identity known as "Qawm," in which community mosques as communal buildings play a crucial role. Additionally, we discovered that ethnicity significantly influenced Kabul residents'preferences for where to live. We reviewed the five master plans created for Kabul City. Early master plans had little involvement from the community and were essentially technocratic and authoritarian. However, in the fourth master plan (2011), there was a turn toward participatory planning. The most recent urban design framework shows an uneven distribution of economic, administrative, and facility hubs across ethnic groups and looks to have declined in terms of participatory planning. In order to sustain communal cohesion, this study recommends that policymakers consider ethnic and sub-ethnic components in urban planning. The study highlights the need for more thoroughylans to address ethnic division to prevent the city from becoming further polarized.博士（工学）琉球大
浅海域に生息するサンゴの生活史に対して水深の与える生理的な影響
Get PDFMesophotic habitats are considered a potential refuge for corals, where they may have a better chance of surviving under ongoing climate change. The variations of temperatures in a mesophotic habitat are lower than those in shallow habitat. However, our knowledge of mesophotic corals' susceptibility and threshold temperatures to cope with rapid climate change is limited. Furthermore, the potential of the shallow corals to acclimate in mesophotic habitats has not yet been well understood. This dissertation investigates the physiological response of eleven shallow and mesophotic species and compares threshold temperatures of corals across depth. Furthermore, the photo-acclimation potential of shallow coral species in different life stages, including larvae, early polyps, and adults, investigates at 5, 10, 20, and 40m depth. Afterward, the transplanted fragments' thermal acclimation and threshold temperature were assessed and compared with shallow fragments in the original depth. This thesis conducts to understand whether shallow coral can acclimate in mesophotic depth and whether we can consider mesophotic depths as refugia for shallow coral reefs or not. Physiological response and survivorship of fragment over thermal experiments showed that mesophotic species are more sensitive to stress, and the threshold temperature of these species are lower than shallow species. In examining the acclimation potential of shallow corals larvae and early recruits, surprisingly, the settlement rates of larvae in different depths were not significantly different between depth and species. The results indicate that the shallow coral larvae and juveniles have depth change's substantial plasticity, such as photo physiological and morphological plasticity. As a result, they can survive at different depths. In addition, photo physiological acclimation was observed in adults of shallow corals to a wide range of light intensities across 5, 20, and 40m depths. Symbiotic algae showed a dramatic increase with decreasing depth in juveniles and adults. Acropora tenuis showed high morphological plasticity across depth in juvenile and adult stages. The fragments of 40m depth showed higher tolerance than shallow fragments. The fragments can keep their thermal tolerance while acclimatizing in dim light. Light in shallow reefs has intensified the negative impact of thermal stress. I conclude that species in the MCEs can survive under low thermal stress. However, mass bleaching and high mortality can be expected when a moderate thermal stress range of 4?8 degree heating weeks is experienced. In addition, shallow coral phenotypic plasticity or generation of multiple performance' outcomes within the shallow coral in different life stages may have acted as a buffer to depth change and a modulator to the evolutionary response.博士（学術）琉球大学University of the Ryukyu